Feature

This content was provided by Warren P. Ruemmele, and is maintained in a database by the ISS Program Science Office.

Brief Summary

The ARCTIC refrigerator/freezer (ARCTIC) provided a thermally-controlled environment for storing biological samples prior to their return to Earth in the early stages of the International Space Station (ISS). The ARCTIC freezers supported several of these experiments on ISS during Expeditions 4 and 5.

ARCTIC provided a middeck-locker-size, EXpedite the PRocessing of Experiments to Space Station (EXPRESS) rack-compatible refrigerator/freezer for a variety of experiments needing temperatures ranging from -22 to +4 °C.

The ARCTIC refrigerator/freezer (ARCTIC) was operated as a refrigerator or freezer aboard the International Space Station (ISS). Cooling was accomplished via thermoelectric elements (which created a heat difference from an electric voltage). The ARCTIC was capable of providing temperatures as cold as -25 °C while operating with ISS water cooling or -12 °C while operating with ISS air cooling.

Two ARCTIC units supported the early biological experiments on the ISS. The first unit, ARCTIC-1, was delivered to the ISS during the 8A (STS-110) mission in April of 2002. The second unit, ARCTIC-2, was launched on UF2 (STS-111) in June 2002. ARCTIC-1 operated as a freezer with a set temperature of -25 °C, while ARCTIC-2 operated in refrigerator mode at 4 °C.

Together, the ARCTIC units operated continuously for 6,870 hours during Expeditions 4 and 5 before malfunctioning and losing the ability to cool. During checkout operations on Expedition 4, ARCTIC-2 was unable to cool to freezing temperatures, but was able to operate at 4 °C. The ARCTIC units were transferred from the space shuttle to EXpedite the PRocessing of Experiments to Space Station (EXPRESS) rack 4 on the ISS. After a brief checkout to begin operations, minimal crew interaction with the ARCTIC units was required to place samples inside the ARCTIC units. The ARCTIC units provided a total of 38 liters of cold stowage on the International Space Station.
Operations

Facility Operations

The ARCTIC units were transferred from the space shuttle to EXpedite the PRocessing of Experiments to Space Station (EXPRESS) rack 4 on the ISS. After a brief checkout to begin operations, minimal crew interaction with the ARCTIC units was required to place samples inside the ARCTIC units. The ARCTIC units provided a total of 38 liters of cold stowage on the International Space Station.

After installation and power up in the EXPRESS Rack, ARCTIC-2 displayed reduced water flow rate which prevented it from cooling to its lowest (freezer or -21ºC) temperature. ARCTIC?s design required liquid (water) cooling to achieve its coldest temperatures, while only EXPRESS AAA cooling was needed to achieve refrigeration (+4ºC) temperatures. It performed adequately as a refrigerator, however. Following the completion of Expedition 5, ARCTIC-2 was returned to Earth on 11A (STS-113). Inspection of the unit showed a piece of plug material from manufacturing had been left in the internal water lines, causing low flow rate of cooling water. Preflight pressure drop checks failed to detect the FOD because the test bench sensor range did not go low enough to catch such a partial flow obstruction. Inspection also revealedignificant corrosion in the heat exchanger area, which caused some thermoelectric cooling elements within the ARCTIC to fail. The corrosion was caused by the inability of the hermetic seals to sufficiently keep out moisture from this heat exchanger area due to a subvendor material error. Following analysis of ARCTIC-2, ARCTIC-1 began to fail and was powered down on board the ISS (Ruemmele 2003).

Based on the analysis of ARCTIC-2, in-flight maintenance (IFM) procedures were developed and uplinked to the crew to attempt a repair of the thermoelectric cooling circuit which was suspected as being the cause of ARCTIC-1 failure. A small repair kit that was flown up on STS-113. As a result of the crew?s IFM it was found that ARCTIC-1 had prevalent corrosion in the area of the thermoelectric elements, but nevertheless a repair was attempted. As a result of incredible effort by the crewmember ARCTIC-1 regained the ability to cool to -5°C but unfortunately malfunctioned again after approximately 24 hours. The second malfunction is believed to have been an outgrowth of the initial malfunction. However, the ability of the crew to repair a unit that was not designed to be repaired on orbit without previous training with the help of streamlined maintenance procedures, demonstrated the ability to carry out unpredicted repairs in space (Ruemmele 2003). It also demonstrated the importance of considering on-orbit maintenance during the design phase of systems intended for extended on-orbit operation. ARCTIC-1 was returned to Earth for assessment on LF-1 (STS-114) in August 2005.

The lessons learned from the operation of the ARCTIC units early in ISS assembly led to improvements of the design of the next generation of cold stowage hardware. The Microgravity Experiment Research Locker Incubator (MERLIN) was re-reviewed to ensure adequacy of its cooling element hermetic seals. Lessons from the IFM were considered during design of the General Laboratory Active Cryogenic ISS Experiment Refrigerator (GLACIER). These lessons were:

Consider on-orbit maintenance during the design phase of systems intended for extended on-orbit operation, even if the system has no formal ORUs. The "ISS IVA Toolbox" is easily reviewed on-line at NASA JSC.

ISS toolkit should always include tungsten and carbide drill bits, screw extractors (aka easy-outs), and offset cruciform and Torx drivers. Also a soldering kit, multimeter, and a selection of insulated wire, resistors, and other small electronic components. Hardened steel drills are completely ineffective for drilling out hardened aerospace grade fasteners. Shaving cream works well to capture drill shavings in microgravity.

In-flight maintenance procedures can be greatly streamlined and more rapidly produced if a "Chilton's Handbook" approach is used that emphasizes stepwise instructional imagery instead of text heavy descriptions. It is a good idea to take many photographs during manufacturing steps in case they are needed later for this and to document as-built condition.

Pre-flight checks must test all corners of the operational envelope and test stand instrumentation range should exceed operational range of unit under test.